Author Topic: de-coke  (Read 115 times)

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« on: 28 October, 2020, 16:14:49 »
Hi, I am about to take off the cylinder head of my M21 to de-coke it. At the same time I plan to re-grind or replace the vavles and springs along with a new head gasket. Is it necessary to put on new piston rings at the same time or will I be able to get away with leaving on the current ones? By not replacing the rings saves me having to take off the barrel which on the M21 is bolted to the crank case seperately from the head which itself has a further 10 nuts. It appears to be possible to grind or replace the valves also without taking off the barrel so I could achieve quite a bit without taking much apart. One niggling issue for me would be that since the new valves will create a better seal, thus higher compression, would this cause problems with rings that are a bit worn?


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Re: de-coke
« Reply #1 on: 28 October, 2020, 17:40:42 »
I don't think it would cause a problem with the rings. But I would want to be completely sure that all grinding paste etc all cleaned off before reassembly.

Not sure how you could do that with the barrel in situ.


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Re: de-coke
« Reply #2 on: 30 October, 2020, 19:23:22 »
It is perfectly normal to do a decoke without removing the barrel. If using a normal amount of grinding paste on the valves a careful wipe with a rag wetted with paraffin or petrol to clean off the paste after grinding should be adequate.